Thermally conductive integrated circuit package with radio frequency shielding

ABSTRACT

A semiconductor device package comprises a substrate (10), a flip-chip (16), an underfill adhesive (25), and a thermally and electrically conductive plastic material (20). A leadless circuit carrying substrate has a metallization pattern (13) on a first side (15), one portion of the metallization pattern being a circuit ground (17). The second side has an array of surface mount solder pads (24) electrically connected to the metallization pattern by means of at least one conductive via (26) through the substrate. A semiconductor device (16) is flip-chip mounted to the metallization pattern by means of metal bumps (22). An underfill adhesive (25) fills the gap between the semiconductor device and the substrate. A thermally and electrically conductive plastic material (20) containing metal particles is transfer molded to encapsulate the semiconductor device, the underfill adhesive, and a portion of the first side of the leadless circuit carrying substrate, forming a cover. The conductive plastic material is electrically connected to the circuit ground to shield the semiconductor device from radio frequency energy, and is mechanically attached to the semiconductor device to dissipate heat. Fins (28) may be molded into the conductive plastic material to further enhance the ability to dissipate heat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Pat. No. 5,153,379 by Guzik et al.,issued Oct. 6, 1992, entitled "Shielded Low-Profile Electronic ComponentAssembly", which relates to an encapsulated electronic component with ametal shield, and to U.S. Pat. No. 5,241,133 by Mullen et al., issuedAug. 31, 1993, entitled "Leadless Pad Array Chip Carrier", which relatesto an encapsulated integrated circuit, and also to U.S. patentapplication Ser. No. 650,326, filed Jan. 31, 1991, which relates to anencapsulated semiconductor device coated with a vacuum deposited metallayer, all assigned to Motorola, Inc.

TECHNICAL FIELD

This invention relates generally to semiconductor device packages andmore specifically to thermally conductive radio frequency shieldedsemiconductor device packages.

BACKGROUND

Semiconductor device packages or integrated circuit (IC) chip carriersfind use in a variety of high-density electronics applications. Theintegrated circuits or semiconductor devices are typically protectedfrom the external environment by transfer molding a thermoset orthermoplastic resin about the device. This package provides protectionfrom dust, humidity and other environmental factors which can destroythe delicate circuitry.

A major problem associated with these types of packages is that they donot provide shielding from electromagnetic radiation, such as radiofrequency interference (RFI) or electromagnetic interference (EMI). Thisability to shield high-frequency circuits, especially in electronicequipment such as two-way radios, is critical. Conventional shieldingsystems are generally characterized by a metallic enclosure constructedto surround the device to be shielded. This enclosure acts either toprotect the electrical equipment from external RFI or EMI signals or toprevent the escape of RFI or EMI signals generated by the device.Typically, these shielded enclosures are made from a conductive materialthat is electrically coupled to an appropriate ground. In the prior art,shielded enclosures have been made by attaching a drawn metallic casingover the transfer molded package and soldering the metal casing to asubstrate connected to the device. Unfortunately, this method ofshielding is costly and cumbersome because of:

A) High temperatures generated during the soldering process forattaching the metal shield to the device. Heat generated by thesoldering process may be conducted directly to the IC and can damage it.Due care is required in order to control the soldering process toprevent jeopardizing the quality of the IC.

B) The additional thickness or bulk required when adding a metalenclosure. The increase in the overall size of the shielded package issubstantial, due to the additional thickness of the shield. This resultsin a package that is larger than optimum.

C) The additional cost associated with the soldering operation. The stepof soldering the shield requires additional assembly time and labor,adding further cost to the final package. Providing shielding forintegrated circuits in this way requires special mounting and holdingfixtures for the shield and the IC package.

Conventional shielded systems also do not provide for dissipation ofthermal energy generated by the device. Numerous methods of heat sinkingare known in the art, and generally comprise attaching a metal heat sinkto the IC package. This approach is not optimal because thermal energymust still travel through the insulating plastic molding compound priorto reaching the metal heat sink. Radio Frequency (RF) power ICs such asamplifiers present special shielding and thermal dissipation problemsthat are not addressed by the conventional art.

As a result, a need exists for a method to provide RFI shielding andenhanced thermal conductivity to a high-density integrated circuitpackage that is economical, does not generate excessive temperatures,and provides a low-profile, high-density package.

SUMMARY OF THE INVENTION

Briefly, according to the invention, there is provided a semiconductordevice package comprising a substrate, a flip-chip, an underfilladhesive, and a thermally and electrically conductive plastic material.A leadless circuit carrying substrate has a metallization pattern on afirst side, one portion of the metallization pattern being a circuitground. The other side of the substrate has an array of surface mountsolder pads electrically connected to the metallization pattern by meansof at least one via or through-hole. A semiconductor device is flip-chipmounted to the metallization pattern by means of metal bumps. Anunderfill adhesive fills the gap between the semiconductor device andthe substrate. A thermally and electrically conductive plastic materialis transfer molded to encapsulate the semiconductor device, theunderfill adhesive, and a portion of the first side of the substrate,forming a cover. The conductive plastic material is electricallyconnected to the circuit ground to shield the semiconductor device fromradio frequency energy, and is mechanically attached to thesemiconductor device to dissipate heat.

In an alternate embodiment of the invention, thermally conductive finsare molded into the thermally and electrically conductive plasticmaterial to provide enhanced heat dissipation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away isometric view of an integrated circuit package inaccordance with the invention.

FIG. 2 is a partial cross-sectional view of FIG. 1 through section 2--2in accordance with the invention.

FIG. 3 is a cross-sectional view of an alternate embodiment of theinvention.

FIG. 4 is a cross-sectional view of a further embodiment of theinvention.

FIG. 5 is a cross-sectional view of an alternate embodiment of theinvention.

FIG. 6 is a block diagram of a radio in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward.

Referring now to FIG. 1, a substrate 10 is provided as a circuitcarrier. The substrate may be made from any one of a number of materialscommonly used in the industry, such as epoxy, polyester, polyimide,polyetherimide, polytetrafluoroethylene, glass-reinforced printedcircuit board material, metal, ceramic, etc., and may be rigid orflexible. Substrate thicknesses vary from approximately 0.02 mm to 7 mm,with thicknesses ranging from 0.1 mm to 2 mm being preferred. Thesubstrate 10 has a metallization pattern 13 on an upper or first side15. The metallization pattern 13 comprises bonding pads 12 thatcorrespond to bond pads on an integrated circuit (IC) 16. One portion ofthe metallization pattern 13 is a grounding pad 17 that comprises acircuit ground.

Referring now to FIG. 2, on a second side of the substrate 10 is aco-planar array of surface mount solder pads 24. The bonding pads 12 areelectrically connected to the surface mount solder pads 24 by means ofconductive through holes 26. The solder pads 24 comprise an attachmentmeans for surface mounting the semiconductor device package 5 to alarger substrate such as a mother board. Surface mounting technologyusing surface mount pads is well known to those skilled in the art andis also referred to as leadless technology. Hence, the semiconductordevice package 5 may also be referred to as a leadless package. Solderbumps 23 may be optionally attached to the solder pads 24 in order toprovide ease of soldering the package to a larger substrate or circuitboard. In another embodiment of the invention, pins 18 may be attachedto the solder pads 24 so as to form a leaded package, or the solder padscould be replaced with pins that fit into holes in the substrate, andare electrically connected to the metallization pattern 13. Suchpackages would then have an array of pins 18 protruding below thesurface of the substrate 10, forming a pin grid array (PGA) package.

An IC 16, such as a semiconductor die or chip, is flip-chip bonded tothe bonding pads 12 and the substrate 10. This mechanical and electricalattachment to the metallization pattern 13 is typically performed bymeans of metal bumps 22. The metal bumps 22 are typically solder bumpsand the IC 16 is attached using controlled-collapse-chip-connection (C4)technology. The metal bumps may comprise solder or may also be othermaterials such as gold, indium, tin, lead, or alloys of these materials.When the IC 16 is flip-chip bonded to the substrate 10, the activesurface of the IC is facing the substrate. There now exists a small gapor space between the IC 16 and the upper surface 15 of the substrate 10.This gap is filled with an underfill material 25 in order to provide amore robust mechanical connection between the IC and the substrate, andto provide environmental protection and electrical isolation to theactive surface of the IC. The underfill material 25 is typically anadhesive, such as an epoxy or an acrylic and has a thermal coefficientof expansion that approximates that of the die and/or the substrate.Examples of underfill materials have been shown in the literature.

The assembly is now encapsulated by placing it into a transfer moldingcavity and transfer molding a thermoplastic or thermoset moldingcompound 20. During this operation, the molding compound 20 flows aroundthe IC 16, encapsulating it. The molding compound 20 also encapsulatesthe underfill material 25 and covers portions or substantially all ofthe upper surface 15 of the substrate 10. Molding compound 20 comprisesa thermally and electrically conductive material, such as an epoxy,having at least one filler, for example, a metallic element or alloy,which substantially contributes to the thermal and electrical conductiveproperties of the molding compound. The molding compound 20 is typicallyfilled to approximately 70% to 75% with copper, aluminum, nickel, gold,silver, or similar type materials to provide electrical and thermalconductivity. Suitable encapsulating materials are sold by Nitto,Sumitomo (1033-B), Nippon Steel, Shinetsu, Ciba-Geigy, Hitachi (EN 4274,or EN 4072), Dexter-Hysol, Dow Chemical, or Shell Chemical.

The molding compound 20 is situated on the upper surface 15 of thesubstrate 10 such that it provides electrical and mechanical contact tothe ground pad 17 and the back surface of the IC 16, which is frequentlygrounded. As shown in FIGS. 2 and 3, ground pad 17 is also electricallyconnected by means of a conductive through hole or via 21 to a surfacemount solder pad 24 on the bottom side of the substrate 10. In this way,the electrically conductive molding compound 20 now forms not only acover for the IC 16, but also provides an EMI/RFI shield around the ICin order to form a shielded package. By shielding the package in thismanner, external metal shields, as taught in the prior art, are nolonger necessary. This solves the problems of the prior art, such ashigh temperatures transmitted to the IC during the shield attachmentprocess and the additional thickness or bulk associated with the shield.

Because the molding compound 20 contains a high amount of metal filler,it is also thermally conductive. The intimate contact between themolding compound 20 and the IC 16 provides a good thermal path todissipate heat from the IC. Prior art packages encapsulated the IC 16with untilled molding compound which comprised a thermal insulator. Thepackage of the instant invention provides improved thermal management ofthe IC 16.

Referring now to FIG. 3, it may be seen that the molding material 20 canbe also formed to provide increased surface area on the top of thepackage. Features such as fins or protrusions 28 may be molded directlyinto the molding compound 20 during the transfer molding operation. Fins28 provide increased surface area in the top of the package that servesto further enhance the heat-sinking capability of the package 5. FIG. 3shows just one of many configurations that the fins 28 may assume. Othertypes of configurations that enhance the surface area of the top of thepackage 5 could provide equivalent thermal performance.

Referring now to FIG. 4, it may be seen that a conventional heat sink 29such as a cast, stamped, or extruded metal structure may be attached tothe top of package 5. Heat sink 29 is typically attached by means of athermally-conductive material 27, such as thermal grease or solder.Because the overmold compound 20 has a high amount of metallic filler,the metal heat sink 29 can be soldered or welded directly to the moldingcompound 20.

In a further embodiment of the invention, the electronic package asdescribed herein may find particular use in portable communicationsapplications. Referring to FIG. 6, the RF shielded thermally conductiveintegrated circuit package 5 of the present invention is utilized in aradio 30 comprising any well-known radio, such as portable two-wayradios manufactured by Motorola Inc., which may operate in eitherreceive or transmit modes. The radio 30 includes a receiver section 31and a transmitter section 32 which comprise means for communicating,that is, transmitting or receiving communication signals for the radio.

In the receive mode, the portable radio 30 receives a communicationsignal via an antenna 33. A transmit/receive (T/R) switch 34 couples thereceived communication signal to the receiver 31. The receiver 31receives and demodulates the received communications signal and presentsits audio component to a speaker 36. It may be appreciated by one ofordinary skill in the art that other functions not herein described maybe provided by any suitable means, including a controller means (notshown), which controls the entire operation of the radio 30.

In the transmit mode, audio messages are coupled from a microphone 37,where they are used to modulate a carrier signal as is well known in theart. The modulated carrier signal is then applied to the antenna 33through the T/R switch 34 for transmission of the communication signal.It may be appreciated that the RF shielded thermally conductiveintegrated circuit package 5, according to the principals of the presentinvention, may be utilized in suitable sections of the transmitter orreceiver sections 32 and 31, respectively.

In summary, a monolithic integrated circuit package is formed,comprising a thermally and electrically conductive epoxy thatencapsulates at least one semiconductor device or integrated circuit inorder to reduce the transfer of unwanted radio frequency energy into orout of the semiconductor package. In addition, the thermally-conductivematerial provides enhanced heat sinking capability in order to providean improved package for flip-chip mounting of power RF die. Theelectrically-conductive molded compound is electrically coupled to apoint on the circuit substrate corresponding to a ground plane and formsan RF shield without subjecting the IC to excessive heat. Fins or otherprojections may be easily molded into the thermally and electricallyconductive molding compound in order to provide improved cooling.

While the preferred embodiments of the invention have been illustratedand described, it will be clear that the invention is not so limited.Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as defined by theappended claims.

What is claimed is:
 1. A semiconductor device package, comprising:aleadless circuit carrying substrate having two opposed sides, a firstside having a metallization pattern, one portion of the metallizationpattern being a circuit ground, and a second side having a substantiallycoplanar array of surface mount solder pads, the metallization patternbeing electrically connected to the surface mount solder pads by meansof at least one conductive via through the leadless circuit carryingsubstrate; an integrated circuit die flip-chip mounted on themetallization pattern and the first side of the leadless circuitcarrying substrate; an underfill adhesive between the integrated circuitdie and the first side of the leadless circuit carrying substrate; and athermally and electrically conductive plastic material transfer moldedto form a cover and encapsulating the integrated circuit die and aportion of the first side of the leadless circuit carrying substrate,the conductive plastic material electrically coupled to the circuitground and forming a radio frequency energy shield about the integratedcircuit die, and mechanically coupled to the integrated circuit die,forming a heat sink to dissipate heat from the die.
 2. The semiconductordevice package of claim 1, wherein the cover is smaller than theleadless circuit carrying substrate, thereby exposing a portion of thefirst side of the leadless circuit carrying substrate about a perimeterof the cover.
 3. The semiconductor device package of claim 1, whereinthe cover encapsulates all of the first side of the leadless circuitcarrying substrate not covered by the integrated circuit die.
 4. Thesemiconductor device package of claim 1, wherein the cover has finsmolded into an upper surface.
 5. The semiconductor device package ofclaim 1, further comprising a metal heat sink attached to an uppersurface of the cover.
 6. The semiconductor device package of claim 1,wherein the thermally and electrically conductive plastic materialcomprises a thermoset resin filled with metal.
 7. The semiconductordevice package of claim 1, wherein the leadless circuit carryingsubstrate is a glass reinforced printed circuit board.
 8. Thesemiconductor device package of claim 1, wherein the leadless circuitcarrying substrate is a flexible film selected from the group consistingof polyimide, polyester, or polyetherimide.
 9. The semiconductor devicepackage of claim 1, wherein the surface mount solder pads are bumpedwith solder.
 10. The semiconductor device package of claim 1, furthercomprising metal pins attached to the surface mount solder pads.
 11. Athermally conductive integrated circuit package with radio frequencyshielding, comprising:a printed circuit substrate having two opposedsides, a first side having a metallization pattern, one portion of themetallization pattern being a circuit ground, and a second side having asubstantially coplanar array of surface mount solder pads, themetallization pattern being electrically connected to the surface mountsolder pads by means of at least one conductive via through the leadlesscircuit carrying substrate; an integrated circuit die flip-chip mountedon the metallization pattern and the first side of the printed circuitsubstrate by means of metal bumps; an underfill adhesive between theintegrated circuit die and the first side of the printed circuitsubstrate; and a plastic material filled with metal particles transfermolded to encapsulate and form a cover for the integrated circuit dieand a portion of the first side of the printed circuit substrate whereina portion of the first side of the printed circuit substrate about aperimeter of the cover is revealed, the cover electrically coupled tothe circuit ground to shield the integrated circuit die from radiofrequency energy, and mechanically coupled to the integrated circuit dieto dissipate heat from the die.
 12. The thermally conductive integratedcircuit package of claim 11, wherein the cover has fins molded into anupper surface.
 13. The thermally conductive integrated circuit packageof claim 11, further comprising a metal heat sink attached to an uppersurface of the cover.
 14. The thermally conductive integrated circuitpackage of claim 11, further comprising solder bumps on the surfacemount solder pads.
 15. An electronic component assembly, comprising:anelectronic component having a plurality of terminals; an electroniccomponent carrier including a substrate having first and second opposedmajor surfaces, and a conductive pattern on the first major surface forreceiving the electronic component, and at least one ground pad on thesame major surface as the conductive pattern; the electronic componentflip-chip bonded to the conductive pattern of said electronic componentcarrier; an underfill adhesive between the electronic component and thefirst major surface; and a thermally and electrically conductive plasticmaterial transfer molded to form a cover and encapsulate the electroniccomponent and a portion of the first major surface, the conductiveplastic material electrically coupled to the ground pad to provide ashield for substantially reducing the ingress or egress of radiofrequency signals through the cover, and mechanically coupled to theelectronic component to dissipate heat from the electronic component.16. A radio, ,comprising a transmitter, said transmitter having a heatproducing amplifier, comprising:a leadless circuit carrying substratehaving two opposed sides, a first side having a metallization pattern,one portion of the metallization pattern being a circuit ground, and asecond side having a substantially coplanar array of surface mountsolder pads, the metallization pattern being electrically connected tothe surface mount solder pads by means of at least one conductive viathrough the leadless circuit carrying substrate; an integrated circuitflip-chip mounted on the metallization pattern and the first side of theleadless circuit carrying substrate by means of metal bumps; anunderfill adhesive between the integrated circuit and the first side ofthe leadless circuit carrying substrate; and a thermally andelectrically conductive plastic material transfer molded to form a coverand encapsulate the integrated circuit and a portion of the first sideof the leadless circuit carrying substrate, the conductive plasticmaterial electrically coupled to the circuit ground to shield theintegrated circuit from radio frequency energy and mechanically coupledto the integrated circuit to dissipate heat from the integrated circuit.